From: William James <w_a_x_man@...>
Date: 2009-02-28T15:09:03+09:00
Subject: Re: Array performance question

Jim Menard wrote:

> Here's a real Array performance mystery. I can't help my friend figure
> this one out. He writes,
> 
> ========
> 
> Is there a known bug in Ruby array performance?  I spent a lot of time
> yesterday boiling down the following example
> 
> 
> http://blogs.codehaus.org/people/geir/archives/001768_baffled_with_ruby.html
> 
> only because I still can't believe I'm not doing something incredibly
> stupid.  (I'm a newbie, "Reluctant Rubyist")
> 
>  I'm just not used to arrays behaving this way :)  Anyone have any
> insight?
> 
> ========
> 
> He'd love a response in his blog, but with permission I'll copy
> answers here over there. He's not a regular ruby-talk reader...yet.
> 
> Jim

This variation exhibits the same behavior.


require 'benchmark'

class BufferContainer

 def initialize( initial_data )
   @buf = initial_data
 end

 def put_array( array )
   @buf[0, array.size] = array
 end
end

size = 999
the_array = (0..4).to_a

(1..3).each{|i|
  size *= 10
  a = [nil] * size

# RUN WITH THIS COMMENTED OUT FIRST
#   a << 9

  puts "size = #{ size } #{ a.size }"
  puts  Benchmark.measure {
    10_000.times {
      buf = BufferContainer.new( a )
      buf.put_array( the_array )
    }
  }

}